The Ubuntu appliance image available at Install Plex Media Server | Ubuntu Appliance | Ubuntu does not discover a USB plugged-in hard drive, at least not with Raspberry.
Making it work turned out to be a PITA because of the ROM nature of Ubuntu Core. I went with the original Raspberry Pi distribution and dpkg’d Plex on it; however I still like the Appliance appraoch. Can you please make it work?
Thanks and best!